The use of half-inch magnetic tape cartridge technology for back-up and archive purposes is well known in the art. Such tapes and drives include those formats known as digital linear tape (DLT®) and linear tape open (LTO™). Both types of tape are popular for back-up, archive and library uses. Both of these formats are read/write capable. The magnetic tape drives are magneto-based. A magneto head moves across a tape as it passes over the head, serpentining down the tape to fill the entire tape with data. A significant difference between the DLT® tapes and the LTO™ tapes is that the LTO™ tapes have a memory chip in the cartridge that allows storage and retrieval of information about the tape and its use. Prior art magneto optic (MO) drives and libraries are also popular for archiving. Magneto optic drives are a read/write device. MO drives allow random access similar to a CD-ROM disk.
The use of write once read many (WORM) storage is desirable for many records, especially for archiving, particularly for archiving financial or confidential information. With the rise of the Internet, many transactions are carried out in day-to-day commerce with no paper or permanent record. This creates problems when customer or legal issues arise. Therefore, a need exists to permanently archive data thereby creating a permanent record. However, an archive medium must have a very large capacity and through-put to handle these transactions.
Data preservation problems have been addressed by the prior art by providing temporary write protection. Floppy disks for example, have write protect notches or lock slides which, can be employed to prevent writing on the media. Therefore, a device can write on the media while the notch is uncovered or a slide is in an unlocked position, and then the notch can be covered or lock slide engaged to make the media “read-only”. Magnetic tape has addressed this problem in a similar manner with a write ring, or in the case of tape cartridges with a record slide switch. These methods all suffer from the same drawback, that is, the mechanism is very easily reversed to make the media writeable once again. Once the media is writeable, data stored thereon can be easily lost as the system overwrites new data onto the previously stored data. Similarly, in most computer operating systems, a file can be marked as read-only after it has been initially written. Again, however, the read-only status is very temporary and can easily be reversed with another operating system command. Because the mechanism is easily reversed in all these cases, there is no audit trail or assurance of data integrity.
A problem in converting traditionally rewriteable media to write-once media is that drives that were manufactured prior to the design of the new WORM media will not understand that the media is WORM and may write on the media even though it has been designated as read-only. Because the previously-manufactured drive is unaware of the mechanism by which the media is converted to read-only, it might ignore such a mechanism and write on or erase the media.
WORM instructions may be embedded in an MO disk. Such that when a particular portion of the disk is read at boot-up, the disk is recognized as a WORM disk and the drive can only write once to any given point on the disk. Such a system and method are disclosed in Curtis, U.S. Pat. No. 5,233,576, which is hereby incorporated herein by reference in its entirety. MO archive media and drives are considerably more expensive per megabyte than tape. Tape is very inexpensive per megabyte, and a tape cartridge can hold more data than MO media.
As pointed out above, the use of memory in a tape cartridge, generally referred to as cartridge memory (CM), is known in the art. Existing cartridges and drives store information in the cartridge memory such as how many times a tape has been loaded, a cassette serial number, what was last written on the tape, what block was last written to on the tape and/or the tape error rate. This information facilitates setting up the tape when it is inserted back into a drive. Thus the drive recognizes the tape format and adjusts itself to read or write the next block. Information in the memory about error rate and/or number of loads can help diagnose failing tapes. Such cartridge memory, also known as memory in cartridge (MIC), was first used by Sony Corporation and is employed in the aforementioned LTO™ format. The use of cartridge memory is also planned in Quantum Corporation's new Super DLT® tapes.
Each time a tape cartridge with CM is inserted into a drive the CM is read during initialization. If there is no cartridge memory reader in the drive, the tape will not function at all. During the drive initialization sequence, the drive reads the memory, diagnoses the tape, recognizes the tape format and where writing should begin.